1. Field of the Invention
The present invention relates to an automatic vehicle braking device, in particular, an automatic vehicle braking device for automatically braking a vehicle when there is a possibility of collision between the vehicle and an obstacle.
2. Description of the Related Art
Vehicle travel safety devices have conventionally been proposed. For example, there has been proposed a device in which travel environment factors about a vehicle, more specifically, the distance (inter-vehicle distance) to a vehicle ahead and the relative speed of the vehicle ahead with respect to one's vehicle are detected. When the distance between one's vehicle and the obstacle (the vehicle ahead) has become smaller than a predetermined distance, there is generated a deceleration (primary braking) capable of letting the driver know that a braking force has been generated by an automatic brake device. When the state in which the distance between one's vehicle and the object (the vehicle ahead) is within the predetermined distance persists for a predetermined period of time, a further deceleration is generated (secondary braking). In the above-described conventional device, the braking force generated to brake the vehicle is basically imparted uniformly to the right and left wheels to thereby brake the vehicle (see JP 2005-041465 A).
In another conventional device proposed, which is a further improvement over the above-described one disclosed in JP 2005-041465 A, the start of the operation of a vehicle occupant protecting device such as a seat belt, and of the brake device, is expedited according to the lap rate when the vehicle is to collide with an obstacle based on width-related information such as the width of the obstacle and its position in the width direction with respect to one's vehicle (see, for example, JP 2005-28992 A).
Further, there has been proposed a device in which, to cope with a situation in which the driver takes a steering avoidance action while a conventional device of the type as disclosed in JP 2005-28992 A is exerting a braking force, the distance between one's vehicle and the obstacle and the relative speed thereof are detected to make a judgment as to whether there is a possibility that they come into contact with each other. When a steering operation performed by the driver is detected in the case in which it is determined that there is a possibility of contact, brake pressure is controlled for each wheel such that the turning property of the vehicle in that steering direction is enhanced (see, for example, JP 07-21500 A).
However, the conventional device as disclosed in JP 2005-041465 A has the following problem. That is, a braking force is generated uniformly in the right and left wheels, which merely produces the effect of reducing the speed of the vehicle. When the vehicle collides with an obstacle while offsetting with respect thereto (hereinafter referred to as offset collision), the damage suffered by the vehicle occupants is more serious as compared with that in the case of a head-on collision.
The conventional device as disclosed in JP 2005-28992 A has a problem in that no consideration is taken of how to cope with a situation in which the driver takes a steering avoidance action while a braking force is being exerted.
On the other hand, when, as in JP 07-21500 A, the turning property of the vehicle is excessively enhanced after the steering avoidance action by the driver, the operational stability of the vehicle may be deteriorated.